How do I make a chance based event

I would like for my enemies to do 1 from 3 actions when the conditions are met, not the 3 but just 1, how can I make that?

Without knowing anything about how your game works I can only suggest that you use the random() expression

I would like for an AI to do 1 of 3 attacks (punching, highpunching and kicking) which requires to turn an event group on, to set an animation and play a sound, the events for an attack are

When A is released : Sprite set animation to Punch_Player, set DamageSpawningGroup active, play sound Punch

thats how an attack works in my game, I would like that when the conditions are met 1 from 3 attacks will be done, how can I make this happen? I was thinking about a time based ''randomness'' where every a timer set to 0.05 seconds will turn an event group on and another one off, + turning another 0.05 timer on and so on, so that every 0.05 seconds when the same conditions are met, there will be a different result, but I suppose this would be cpu intensive and event consuming

You should also take a look at the Timer behavior

Or even better, Rexrainbow's Duration plugin. It allows you to have timers running in each object, it's one of the most useful plugins IMO

The way you explain could be done this way:

Add Global variable "Groups"

system every 0.05 seconds

set variable Groups to : choose(1,2,3)

set group1 deactivated

set group2 deactivated

set group3 deactivated

-- If variable groups is 1

set group1 activated

-- If variable groups is 2

set group2 activated

-- If variable groups is 1

set group3 activated

It would probably be much easier to call a function on attack with a parameter set to choose(1,2,3) and base the attack on the parameter, but well..